To my recollection, my new 1978 Monza Spyder that I purchased new had square seat belt guides. It had black vinyl seats with the honeycomb insert. I'm seeing the triangular guides are more common and plentiful. Can anyone confirm I should have the square seat belt guides for my 78 project?

I can't speak for Monza's but on the other divisions H-body's it seems to be Model and or interior level dependant. My 77 Astre's all had the Delux interior and had Triangle style guides, the 79 Starfire had square Guides.

I had thought that all of my H-Bodies had the square ones, but, I found some triangular ones recently while "Putsing" around on this one, and they seem a better colour match than the others that were included.So maybe Jeff is onto something there. My car has the all vinyl/Grotesque interior well what is left of this faded Red Mess. Harry

I'm not a hoarder I'm a preservationist 78 Monza Spyder (Soon To Be 2+2 with Spoilers)

It's possible I suppose. My '79 sunbird with the cloth interior has the square ones, while my '80 sunbird with the oyster vinyl interior has the triangle ones. They are both sunbird sport coupe models.

I am 99% sure that most 77 and up GM cars switched to the triangle version. I have owned a few 77 Monza's and one 77 Vega and they all had the triangle version. Never owned a 76 Monza so can't speak for it, but my 76 Vega's have the square version.

Looking at the part number for the black triangle version 9737575 shows it fitting most 77 and later GM cars while the square version, part number 1708119 fits 76 and earlier. I am using gmpartswiki to verify.